The present invention relates to dispersed resins used in coating compositions such as paints.
In recent years, apart from emulsion paints, there has been an increase in demand for water-based paints. These paints are prepared by emulsifying the resin or other film forming materials and incorporating pigment, if appropriate, in the emulsified composition. In order to assist the emulsification it is common practice to incorporate a surfactant. However, one of the problems associated with the use of a surfactant is that although it does facilitate the emulsification of the resin it also has a tendency to make the resulting coating more susceptible to water penetration. This is particularly noticeable when the water-based paint is applied over a ferrous metal because in damp conditions rust will form under the coating. The surface activities of the surfactant causes this effect. Thus the very property which makes the surfactant useful in preparing the formulation has an adverse effect on the coating produced from it.
It has now been found, surprisingly, that a particular surfactant system, while being effective in the emulsification of resins and the like, subsequently loses its surfactant effect such that the deleterious effect of ordinary surfactants is not observed or greatly reduced.
An aqueous composition which comprises a reaction product of
(i) at least one carboxylic acid containing from 3 to 22 carbon atoms; and
(ii) at least one unsubstituted or substituted aliphatic amine or polyfunctional aromatic amine, containing from 2 to 25 carbon atoms;
(iii) a complex crosslinking agent of a metal which is zinc, aluminium, titanium, copper, chromium, iron, zirconium or lead.
(iv) a resin or oil, the weight ratio of the resin or oil to the sum of (i), (ii) and (iii) being at least 2.5:1; and
(v) a thickener, a continuous dry layer obtained by applying the composition to Western Red Cedar providing a contact angle with water not exceeding 80xc2x0.
The upper limit of the resin or oil (hereafter referred simply as the xe2x80x9cresinxe2x80x9d) is not particularly critical but, in general, the weight ratio will be from 2.5:1 to 100:1 or more. More usually the weight ratio is from 5:1 to 75:1 and, in particular from 10:1 to 60:1. The preferred ratio will depend on the type of coating composition for which the emulsified resin is intended. A particularly preferred range for a primer will be from 2.5:1 or 2.6:1 to 20:1 while for a paint it will be from 30:1 to 50:1.
It will be understood that the emulsified resin formulation can be used as such as a coating composition or the usual ingredients such as pigments can be incorporated.
It will be appreciated that components (i) and (ii) are reacted together. In some instances, in particular where the acid is solid, it is necessary to cause the components to react, typically by melting the solid acid (solid amine is generally readily water-soluble). Subsequently i.e. once the composition has been applied to the substrate, the crosslinking agent will react with this reaction product, thus making the coating more resistant to water penetration.
The time taken for the coating to dry will, of course, depend on various factors such as the water content and atmospheric conditions. Typically, though it will be dry in 24 hours by which time the crosslinking agent will have reacted with the reaction products of (i) and (ii). Substantial crosslinking occurs in a significantly shorter time than this. For example 80% crosslinking can occur in 6 hours.
In order to prevent premature reaction of the crosslinking agents, the composition should be stored in a confined space before use.
Typically, the solids content of the emulsified formulation will vary from 15% to 75% by weight, generally from 25% to 75% by weight and, more particularly, from 35% to 55% by weight. The concentration of the reaction product will generally be from 0.1 to 10%, preferably from 0.5% to 3%, especially 0.5 to 1.5%, by weight.
Typical resins which can be used in the present invention include silicones, alkyd resin, rosin esters, polyurethanes and acrylic polymers. Oils can be used in place of these resins. It will be appreciated that in some formulations it is desirable to use a combination of these in order to obtain particular effects. In particular for primers, it is preferred to use two different types of resin, for example an alkyd resin and a rosin, such that one of the resins penetrates the substrate somewhat, for example the alkyd resin, while the other stays on the surface, for example the rosin, and acts as a xe2x80x9ckeyxe2x80x9d for the subsequent paint layer.
The silicone resins used in the present invention will generally have the formula
Mxcex1Dxcex2Txcex3Q67 (OR)xcex5xe2x80x83xe2x80x83(I)
where, M=R1R2 R3SiO1/2 D=R4R5SiO2/2 T=R6SiO3/2 Q=SiO4/2R1, R2, R3R4R5 and R6, which can be the same or different, represent a C1-C12 especially C1-C8, hydrocarbon radical
R: a hydrogen atom or a linear or branched C1-C4 alkyl radical,
the copolymer comprising at least one T or Q grouping;
the symbols xcex1, xcex2, xcex3, xcex4 representing, independently, numbers corresponding to the number of atoms of silicon of the type M, D, T and Q relative to an atom of silicon of in the resin of formula (I); the symbol xcex5 representing the molar fraction of the ends xe2x89xa1SiOR relative to an atom of silicon the resin of formula (I); these symbols having the following limits:
xcex1: 0 to 0,5
xcex2: 0 to 0,95
xcex3: 0 to 0,9
xcex4: 0 to 0,8
xcex5: 0,05 to 2
with a xcex1+xcex2+xcex3+xcex4=1.
The groups M can be the same or different when more than one is present; similar comments apply to the groupings D and T. Likewise the groupings OR can be the same or different.
According to a preferred mode of the present invention, the resin is a copolymer of formula (I) where R1 to R6, which are the same or different, represent a C1-C8 linear or branched alkyl radical, R is a hydrogen atom or a C1-C4 linear or branched alkyl radical the copolymers containing at least one T grouping (the symbol xcex3 being a number other than 0) associated with one or more groupings M and D.
Preferred resins are those of formula A and B below:
A: copolymers Mxcex1Dxcex2Txcex3Q67 (OR)xcex5(II) where
A1. according to a first definition:
R1 to R6 C1-C8 identical or different alkyl radicals;
R: a hydrogen atom or a C1-C4 alkyl radical
xcex1: 0,1 to 0,3
xcex2: 0,1 to 0,5
xcex3: 0,4 to 0,8
xcex5: 0,08 to 1,5
with xcex1+xcex2+xcex3=1.
A2. according to a second definition:
R1 to R6: C1-C3 alkyl radicals
R: a hydrogen atom or a C1-C4 alkyl radical
xcex1: 0,1 to 0,3
xcex2: 0,1 to 0,5
xcex3: 0,4 to 0,8
xcex5: 0,08 to 1,5
with xcex1+xcex2+xcex3=1.
B: The copolymers Dxcex2Txcex3(OR), (III) where
B1. according to the first definition:
R4 to R6 which may be the same or different represent C1-C8 linear or branched alkyl radical;
R: a hydrogen atom or a C1-C4 linear or branched alkyl radical, at least 25% of one or more of the substituents R4 to R6 being a C3-C8 linear or branched alkyl radical.
xcex2: 0,2 to 0,9
xcex3: 0,1 to 0,8
xcex5: 0,2 to 1,5
B2. According to a more preferred definition:
R4 and R5: which are the same and represent a C1-C2 alkyl radical,
R6: a C3-C8 linear or branched alkyl radical;
R a hydrogen atom or a C1-C3 linear alkyl radical,
xcex2: 0,2 to 0,6
xcex3: 0,4 to 0,8
xcex5: 0,3 to 1,0
In general each of radicals R1 to R6 can be a linear or branched alkyl radical, for example methyl, ethyl, propyl, butyl or isobutyl; an alkenyl radical such as vinyl; an aryl radical such as phenyl or naphthyl; an arylalkyl radical such as benzyl or phenylethyl; an alkylaryl radical such as tolyl or xylyl; or an araryl radical such as biphenyl.
Typical alkyd resins can be used in the present invention include both drying and non-drying alkyd resins. Thus suitable alkyd resins include oil type using oils having a long carbon chain, eg. C16-C22, especially C18, and typically one or two unsaturated double bonds such as linseed oil, soya oil or safflower oil, which are preferred along with blown rapeseed oil, castor oil, coconut oil and cottonseed oil and alcohol type alkyd resins, using alcohols such as pentaerythritol and glycerol or a mixture of alcohols, together with modified alkyd resins such as with a urethane, phthalic anhydride, isophthalic acid or a hydroxylated polyester or an oil free alkyd.
Other resins which may be used in the present invention include rosin esters, which are preferred, polyurethanes, acrylic polymers, epoxy resins, urea/formaldehyde resins and melamine resins. Typical examples of suitable rosin esters which can be used include those derived from triethylene glycol, which is preferred, glycerol esters, pentaerythritol esters, and diethylene glycol esters along with liquid rosins and esters of modified or polymerised rosins.
Suitable oils which can be used include fatty oils and drying oils such as linseed oil, rape seed oil, fish oil, sunflower oil, and safflower oil, which are preferred, as well as corn oil, soya oil, tung oil and dehydrated oils such as castor oil, hydrocarbon/mineral oils such as paraffin oil, white oil and process oils, and essential oils such as lavender oil, which is preferred, as well as rose oil and pine oil. Silicone oil may also be used.
In the compositions used in the present invention, the complex crosslinking agent will contain one or more metals Naturally, the metal should be chosen so that it does not react with the resin employed. The crosslinking agents contain zinc, aluminium, titanium, copper, chromium, iron, zirconium and/or lead.
The crosslinking agent may be a salt or complex of the metal(s). The salts may be acid, basic or neutral. Suitable salts include halides, hydroxides, carbonates, nitrates, nitrites, sulphates, phosphates etc.
The preferred crosslinking agents are zirconium complexes, for example those described in GB-1002103, which are salts of the zirconyl radical with at least two monocarboxylic acids, one acid group having from 1 to 4 carbon atoms, the other having more than 4 carbon atoms, which may be made by refluxing the carboxylic acid of 1 to 4 carbon atoms with a zirconyl carbonate paste and then adding the carboxylic acid having more than 4 carbon atoms. Water-soluble inorganic metal compounds may also be used. Ammonium zirconium carbonate is particularly preferred.
Typically the metal complexing agent is used in roughly stoichiometric amounts relative to the amine/acid reaction product. Generally the amount of metal complexing agent should not exceed the stoichiometric amount as increasing the amount tends to decrease the stability of the coating composition. In general the mole ratio of metal to reaction product is from 1:1 to 0.1, generally 0.75 to 0.2, and preferably 0.6 to 0.4. If the amount is reduced too much the coating composition does not produce enough water resistance.
The carboxylic acid is an optionally substituted, e.g. by hydroxy, straight or branched chain, saturated or unsaturated C3-C22, preferably C10-C18, fatty acid, e.g. oleic, isostearic, stearic, ricinoleic or tall oil fatty acid.
The unsubstituted or substituted aliphatic amine or polyfunctional aromatic amine is preferably water-soluble in order that a water-dispersible compound is produced when it is reacted with the carboxylic acid. It may be a primary, secondary or tertiary amine optionally substituted, e.g. by one or more hydroxyls, or in the form of an amide, e.g. an amide of the formula
Rxe2x80x94C(O)xe2x80x94NR1R2
where R, R1 and R2 each represent hydrogen, or an optionally substituted alkyl group of 1 to 5 carbon atoms. Suitable substituents for the above optionally substituted groups include halogen, hydroxy or an alkyl group preferably with from 1 to 5 carbon atoms.
Examples of suitable amines and substituted amines include: ethylamine, 2-amino-2-methyl-propan-1-ol, diethylamine, triethylamine, 2-amino-2-ethyl-propane-1,3-diol, 3-amino-1,2-propane-diol, formamide, acetamide, N-ethyl-acetamide, N,N-dimethyl-butyramide, hydrazine, hexamethylene-diamine and tris-hydroxy-methyl-amino methane.
As one of skill in the art will appreciate, the particular combination of acid and amine should be selected depending on the resin to be used and the solids content desired. The nature of the acid determines whether the reaction product is solid or liquid. A solid reaction product has limited solubility so that less can be used but is useful for resins which are difficult to emulsify, for example rosin. In contrast reaction products of liquid acids and solid amines can be used for high solids contents, for example for alkyd resins.
The thickener is an essential ingredient of the composition in order to increase its viscosity and thus the brushability of the coating composition and also reduce penetration of the composition below the surface of the substrate to be treated. The thickener is generally present in an amount of at least 0.1% by weight. Typically the thickener will be present in an amount from 0.1 to 5%, especially from 0.3 to 4%, although for primers the concentration will generally not exceed 1% by weight. Suitable thickeners include polyurethanes, especially non-ionic water-soluble polyurethanes, celluloses, such as hydroxy ethyl cellulose, and xanthan gum, acrylic thickeners e.g. alkali soluble polyacrylate emulsions and chelate thickeners such as ammoniacal zirconium compounds, which are preferably present in an amount from 0.3 to 2% by weight, and clay, preferably present in an amount from 1 to 4% by weight.
It will be appreciated that the compositions of the present invention are intended principally as primers and undercoats. Accordingly, the resulting coating must be appropriate to receive a top coat. For this purpose the surface must not, of course, be water repellent. Thus the contact angle between the substrate and water should not exceed 80xc2x0 The contact angle generally should not exceed 600 and preferably not more than 50xc2x0. Thus typically, the contact angle is 60xc2x0 to 30xc2x0, especially 55xc2x0 to 35xc2x0.
The contact angle can be determined by first applying a continuous layer of the composition to a wood sample. For this purpose Western Red Cedar, of good condition, which had been planed can be employed as the substrate. This is then coated with the composition to provide a good continuous layer. This is generally best achieved by applying two coats of the composition. Obviously the maximum amount which can be applied will vary with the formation but it is sufficient that the wood is well covered by it. The coat or coats should be allowed to dry before the contact angle is measured. The contact angle can be determined using, for example, a Kruss contact angle meter G1, having applied to the surface a droplet of water which had been distilled once. Measurements should be taken once equilibrium has been reached. This will vary with the wood sample. In many instances, equilibrium is reached with 3 to 5 minutes but, in some cases, a longer time, for example about 30 minutes, is required. In order to allow for variations in the wood surface, it is desirable to take 5 measurements and calculate the mean value.
Other ingredients which can be present either in the emulsified resin or oil formulations or in the resultant coating composition include pigment and dyes, typically in an amount from 3% to 30% by weight, anti-corrosive agents such as zinc phosphate, typically in an amount from 2% to 5% by weight, extenders such as calcium carbonate, silica, barytes and talc, typically in an amount from 1% to 30% by weight, bentonite in an amount up to about 1% by weight, biocides in an amount up to 1% by weight, wetting agents such as phosphate esters in an amount up to 0.5% by weight, coalescing agents such as butyldiglycol, typically in an amount up to about 5% by weight, antifoam agents, typically in an amount up to 0.5% by weight, anti oxidants, typically in an amount up to 0.5% by weight, and adhesion promoters such as an acrylic latex, typically in an amount from 1 to 10% by weight and waxes including petroleum waxes such as paraffin wax (refined, partially refined or unrefined), microcrystalline wax and slack wax, vegetable waxes such as montan wax, carnauba wax and candellila wax, animal wax such as beeswax or shellac wax, hydrocarbon mineral wax such as ceresin, synthetic wax such as polyethylene wax and mixtures of waxes, for example paraffinic and microcrystalline wax mixtures. For masonry paints and the like, small grits and fillers customarily used in such paints can be incorporated, for example china clay, titanium dioxide and silicas. Depending on the nature of the resin, it may be desirable to include crosslinking agents such as melamine resins for non-drying alkyd resins along with drying agents based on metals such as cobalt, zirconium, zinc, calcium, lithium, manganese, aluminium and lead, for example cobalt or zirconium octoate.
The balance of the composition is, of course, water.
In order to prepare the emulsified resin compositions of the present invention, typically, the amine and acid are heated in water to, say, 75xc2x0 C. to 80xc2x0 C. and then homogenised. The resin is then added along with the thickener and any additives and the mixture is allowed to cool before the metal complex is added. For conversion into a coating composition pigments and the like are added and the mixture homogenised.